1. 1. Field of the Invention
This invention pertains to a blood contacting membrane which operates as part of a pumping mechanism for displacement of blood through an artificial ventricle. More particularly, the present invention relates to a single layer, pumping membrane wherein one side of the pumping membrane constitutes the blood contacting diaphragm surface within the blood chamber of the ventricle.
2. Prior Art
Despite the growing need for an effective artificial ventricle to replace damaged heart organs, a commercially acceptable artificial ventricle remains a subject of considerable research and development, rather than commercial production. Certainly, many various ventricle designs have been offered for patient use; however, the state of the art continues to be primarily exploratory.
Numerous obstacles remain with respect to achievement of an artificial ventricle which can take its place in the medical community as a standard commodity. One such obstacle is the high cost of such devices, often placing them beyond the reach of day to day economic reality. This high cost arises because of the difficulty in manufacturing an acceptable pumping diaphragm which has minimal stress as it displaces between extended positions at systole and diastole. This stress occurs at folding sections of the diaphragm as it moves from full blood chamber expansion at diastole, through intermediate folds and deformation, to full inverse extension in systole. If these folds and deformations become localized at specific areas of the diaphragm, such areas may weaken as the localized deformations continue for millions of repetitions.
Numerous designs have been attempted which generate broad folding patterns which will avoid localized stress. U.S. Pat. No. 4,974,729 teaches the advantages of using elliptical pumping and blood diaphragms to develop more favorable folding patterns. U.S. Pat. No. 4,981,484, by the same inventor, further developed the elliptical diaphragm with a unique modification to curvature by flattening sections of the diaphragm to program a large fold pattern. Each of these designs utilized multiple membranes for forming the pumping diaphragm, because such a thin membrane minimizes the stress arising as it goes through its deformation.
More importantly, these membranes were molded with a downward curvature, corresponding to the shape of the diaphragm at diastole. This technique and diastole pattern has been virtually universal with respect to membranes formed within a rigid ventricular housing wherein the membrane displaces into a pumping chamber in concave form and extends upward into the blood chamber in convex configuration.
Because the membranes are molded in the downward or diastolic configuration, the perimeter is typically formed with an inverted U-shaped edge, with the outside leg of the U being the point of attachment to the outer housing. In this diastole configuration the membrane has no stress arising, because its molded shape is in original form as originally molded. Upon deformation of the diaphragm upward toward systole, the polymer shape is modified and the natural resilience of the elastomer will tend to increase the stress load to return the membrane to its original, downward configuration. This repeated occurrence of stress within the membrane tends to weaken the polymer at the points of local stress, and will eventually result in diaphragm failure.
This traditional pattern of forming the pumping diaphragm in a downward or diastolic configuration was also adopted in U.S. Pat. No. 4,089,020. This invention disclosure shows a monoseptal, biventricular design wherein the separating wall between the ventricles serves as a rigid support to opposing pumping diaphragms. As is noted in FIG. 7, both diaphragms are biased to a collapsed configuration against the rigid wall in the diastolic position, and must be inflated to realize the systolic mode.
Accordingly, a major problem persists with respect to management of elastic stress associated with diaphragm displacement during the repeated pumping cycle of the artificial ventricle. The existence of this stress required the use of multiple diaphragms in larger ventricles to maintain a sufficiently thin dimension so that elastic stress was minimized. Manufacture of such membranes required repeated dip molding, taking many days to complete fabrication. The total process resulted in extreme high cost in the production of an acceptable membrane for use as a human prosthetic. This high membrane cost contributed to a cost of an artificial heart reaching in the hundreds of thousands of dollars.